What's more, those fit folks who do manage to find themselves under the weather experience a less severe infection than their unfit counterparts. It's all sounding good so far, but, as the BBC reports, there is a small peculiarity (emphasis ours):

For their study, US researchers asked the healthy volunteers to keep a record of any coughs and sniffles they experienced over a three-month period during the autumn and winter.

The volunteers were also asked to say how frequently in any given week they would do exercise lasting at least 20 minutes and intensive enough to break a sweat.

...the most significant factors that cut colds was how much exercise a person did and how fit they perceived themselves to be.

So, in reality, all you need to do is think you're fit to enjoy a lowered risk of colds. You could try all manner of self-deception in an effort to make yourself think you're in shape—or you could go the tried-and-true route and exercise. Either way, this is the kind of information that comes in handy when you're looking for a little motivation to stay in shape this winter.